Abstract:
Nuclear factor (NF)-kB is a transcriptional factor known to mediate the inducible expression of a wide variety of genes that are involved in inflammatory and other cytotoxic reactions in various cell types. Depending on the cell type, NF-kB is activated by diverse stimuli including bacterial lipopolysaccharide (LPS), reactive oxygen species (ROS) and cytokines such as tumor necrosis factor-alpha (TNF-a). In addition, antioxidants have been shown to block NF-kB activation in certain cell types. This observation has led to the hypothesis that NF-kB activation is mediated by ROS in all cell types and in response to all stimuli. In the present study, this hypothesis was tested using calf pulmonary arterial endothelial (CPAE) and normal rat kidney epithelial (NRK52E) cell lines. NF-kB was found to be activated by LPS, TNF-a and pro-oxidant metal chromate [Cr(VI)] in both cell types. In CPAE cells, antioxidants either blocked or reduced LPS, TNF-a and Cr(VI)-induced NF-kB activation consistent with the ROS hypothesis. In contrast, antioxidants had no effect upon NF-kB activation in NRK52E cells. Furthermore, in NRK52E cells, the intracellular calcium chelator, Quin-2AM, significantly attenuated LPS-induced NF-kB activation whereas it had no effect upon NF-kB activation in response to Cr(VI) or TNF-a. These results suggest that NF-kB may be regulated via stimulus-specific pathways in the NRK52E cells. The summation of these results challenged the universal ROS-mediated NF-kB hypothesis and provides evidence for cell type and potentially stimulus-specific NF-kB activation pathways.